150 
( Psathyrella) ampelina , Speira densa , 11. sp., $. dematophorce, n. sp., and 
Cryptocoryneum aure-um , n. sp.—E ffie A. Southworth. 
Ward, H. Marshall. Croonian Lecture : On some Relations between 
Host and' Parasite in certain Epidemic Diseases of Plants. Bead 
February 27,1890. Proc. Royal Society, London, vol. 47, No. 290, 
pp. 393-443, figs. 15.* 
The study of plant diseases has shown rapid progress during the past 
decade and disciples of this branch of botany have reason to hope for 
still greater progress in the near future. Few, however, would have 
supposed that a work of the scope and value of the one before us would 
be possible at the present day. Prof. Ward has long been justly famed 
both for his successes in original investigations and for his happy fac¬ 
ulty in expressing his results in the most lucid English. In the present 
lecture the author treats one of the most difficult, and at the same time 
one of the most important, subjects in the range of vegetable pathology. 
The introduction deals with the general subject of the relations existing 
between host and parasite. The author shows the close connection of 
normal life processes (physiological) and the abnormal ones (patholog¬ 
ical), and insists that students in each branch must know what those 
in the other are doiug. Then the behavior of the normal tissues is 
taken up and the fundamental processes going on in living cells are 
sketched. 
The next section is concerned with the death of the cell, the author 
concluding with the following paragraiffi: 
Between tlie normal life, i. e., the condition of affairs where the life processes are 
going on actively, and the state of permanent death, then, there are all possible gra¬ 
dations; many of these gradations coincide with the phenomena of disease—patho¬ 
logical conditions—and it is toward this difficult domain that I have now to carry 
the discussion. 
Then the variations in environment as effecting the physiological 
processes in the host are considered, and the consequences of variations 
in temperature, in intensity of light, in the amount of aqeuous vapor in 
the atmosphere, etc., are shown. What is of special interest to workers 
in plant diseases is that the effects of these variations as predisposing 
causes to certain diseases are explained. The case is considered of a 
herbaceous plant growing in midsummer, which has previously been 
well supplied with heat and light. Then suddenly cold, dark, rainy 
weather sets in, and as a neb result the parenchymatous tissues are par¬ 
ticularly tender and watery, the cell walls thin and soft, the protoplasm 
more permeable and less resistant; the cell sap contains a larger amount 
than usual of organic acids, glucose, and soluble nitrogenous materials. 
After rapidly sketching the state of our knowledge of the species of 
Botrytis which may under some circumstances cause widespread epidemics 
* The number containing the article can he obtained from Harrison & Sons, 45-46 
St. Martin’s Lane, London, W. C., England, for 1 shilling 6 pence. 
